public class CandidateKey {

	// This method acts as a uniqueness checker for the Candidate object based on the Email__c field
	public static void hasCandidateDuplicates(Candidate__c[] candidates){
	
        	//TODO: Define a map for unique Candidates called "candidateMap" that maps a String to the Candidate
		Map <String,Candidate__c> candidateMap = new Map<String, Candidate__c> ();
		//TODO: Declare a for loop to cycle through the candidates.
		for (Candidate__c candidate: candidates) {
			if (candidate.email__c != null) {
				String ukey = candidate.last_name__c + candidate.email__c;
				if (candidateMap.containsKey(ukey)) { 
					candidate.addError('Candidate with this email already exists in the system');
				}
				else candidateMap.put(ukey,candidate);
			}	
		}

            		// TODO: Within that loop, check to verify that the email is not null and if it has a value, store the lastName+email in a String called "uKey"
			// and then check to see if there are duplicate uKeys within this batch of records.  If there are, use addError to prevent them,
			// and if not, add the uKey/candidate combo to the candidateMap.


		
  		//Now hit the DB looking for dupes
  		if (!candidateMap.isEmpty()){
	  		for(Candidate__c[] candidatesCheck:[select Id, unique_key__c from Candidate__c where unique_key__c IN :candidateMap.keySet()]) {
				for(Candidate__c candidate:candidatesCheck) {
	  				String currentCandidateId = candidate.Id;
	  				//if there's a dupe and this isn't the current record, then add the error.
	  				if(candidateMap.containsKey(candidate.unique_key__c) && (currentCandidateId != candidateMap.get(candidate.unique_key__c).Id)) {
	     				candidateMap.get(candidate.unique_key__c).addError('Duplicate LastName + Email found in salesforce(id: ' + candidate.id + ')');
	  				}
	  			}
	    		}
  		} 
  	} 
}